fix(hydrate): make R inferable from options.layers - #81
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hydrate's element parameter was locked to
`Element<A, never, RendererContext | ControlCtx | SuspenseBoundaryCtx>`,
which meant any element that also required a user-provided service
(NavigationContext, RouteDataProvider, etc.) had to be cast — `as never`
or `as unknown as Element<HTMLElement>` — even though `options.layers`
was providing exactly those services at runtime.
HydrateOptions and hydrate are now generic over `R`. Whatever services
`options.layers` provides show up as the element's `R`, so the intended
pattern typechecks with no casts:
hydrate(App(), root, { layers: Platform.makeClientLayer(router) });
Removed the now-obsolete casts from:
- packages/create-effex SSG + SSR templates
- apps/docs/src/client.ts
- packages/dom's own hydrate regression test
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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…layers
Follow-up: the earlier commit made `R` generic but relied on TS inferring
`R` from both element and options — so passing `hydrate(NeedsFoo(), root)`
without any layers still compiled (R widened to Foo, but options was
undefined). No compile-time protection against forgetting a service.
Refactored so `L` is inferred solely from `options.layers`, and the
element's `R` position is `NoInfer<Layer.Layer.Success<L>>`. Inference
flows one way — layers in, element requirements out. Forgetting to
provide a service the element uses is now a type error.
Matrix of behaviors, all verified:
- element needs Foo, no options → ERROR
- element needs Foo, options={} → ERROR
- element needs Foo, wrong layer provided → ERROR
- element needs Foo+Bar, only Foo layer → ERROR
- element needs Foo, correct layer → OK
- element needs Foo+Bar, merged Foo|Bar layer → OK
- element needs nothing extra, no options → OK (2-arg call still works)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Type-signature follow-up to #78. Two problems fixed:
1. The original type error the user reported.
hydrate's element parameter was locked toElement<A, never, RendererContext | ControlCtx | SuspenseBoundaryCtx>, so any element that also required a user-provided service (NavigationContext,RouteDataProvider, …) had to be cast —as never/as unknown as Element<HTMLElement>— even thoughoptions.layerswas providing exactly those services at runtime. Build still worked (types don't affect runtime), but the error was noisy.2. Casts hide missing layers. The first attempt at this PR (
Rgeneric + inferred bidirectionally) let TS widenRfrom the element's requirements. Sohydrate(NeedsFoo(), root)with nooptions.layersstill compiled — TS inferredR = Foo, options was undefined, no error surface. That's the exact footgun the cast was creating.Fix:
HydrateOptionsandhydrateare now generic over the layer typeL. Inference flows one way —Lis inferred solely fromoptions.layers(viaNoInferon the element'sRslot), then the element must fitFramework | Layer.Layer.Success<L>. TS extracts the layer's provided services and requires the element's requirements to be covered by them.Behavior matrix (all verified)
options.layersFooFoo{}FooBarLayerFooFooLayerFoo | BarFooLayerFoo | BarLayer.merge(FooLayer, BarLayer)Users get type-level assurance that every service the element uses is provided.
Also
Removed the now-obsolete casts from:
packages/create-effexSSG + SSR templatesapps/docs/src/client.tspackages/dom's own hydrate regression test (was usingas neverfor the same reason)Test plan
packages/dom+packages/routersuite: 465 passedapps/docswith a scratch typecheck fileapps/docstypechecks clean with no casts🤖 Generated with Claude Code